How does adaptation differ from mitigation? And what is REDD? The jargon of climate change can be hard to grasp. Use this glossary to decode it.

A

Adaptation Action that helps cope with the effects of climate change - for example construction of barriers to protect against rising sea levels, or conversion to crops capable of surviving high temperatures and drought.

Adaptation fund A fund for projects and programmes that help developing countries cope with the adverse effects of climate change. It is financed by a share of proceeds from emission-reduction programmes such as the Clean Development Mechanism.

Annex I countries The industrialised countries (and countries in transition to a market economy) which took on obligations to reduce their greenhouse gas emissions under the Kyoto Protocol. Their combined emissions, averaged out during the 2008-2012 period, should be 5.2% below 1990 levels.

Annex II Countries which have a special obligation under the Kyoto Protocol to provide financial resources and transfer technology to developing countries. This group is a sub-section of the Annex I countries, excluding those that, in 1992, were in transition from centrally planned to a free market economy.

Aosis The Alliance of Small Island States comprises 42 island and coastal states mostly in the Pacific and Caribbean. Members of Aosis are some of the countries likely to be hit hardest by global warming. The very existence of low-lying islands, such as the Maldives and some of the Bahamas, is threatened by rising waters.

AR4 The Fourth Assessment Report produced by the Intergovernmental Panel on Climate Change (IPCC) published in 2007. The report assessed and summarised the climate change situation worldwide. It concluded that it was at least 90% likely that the increase of the global average temperature since the mid-20th Century was mainly due to man's activity.

AR5 The Fifth Assessment report from the Intergovernmental Panel on Climate Change (IPCC) was published over 2013 and 2014. It says scientists are 95% certain that humans are the "dominant cause" of global warming since the 1950s.

Atmospheric aerosols Microscopic particles suspended in the lower atmosphere that reflect sunlight back to space. These generally have a cooling affect on the planet and can mask global warming. They play a key role in the formation of clouds, fog, precipitation and ozone depletion in the atmosphere.

B

Bali action plan A plan drawn up at the UN Climate Change Conference in Bali, in December 2007, forming part of the Bali roadmap. The action plan established a working group to define a long-term global goal for reduction of greenhouse gas emissions, and a "shared vision for long-term co-operative action" in the areas of mitigation, adaptation, finance and technology.

Bali roadmap A plan drawn up at the UN Climate Change Conference in Bali, in December 2007, to pave the way for an agreement at Copenhagen in 2009 on further efforts to reduce greenhouse gas emissions after the expiry of the Kyoto Protocol. The roadmap gave deadlines to two working groups, one working on the Bali action plan, and another discussing proposed emission reductions by Annex I countries after 2012.

Baseline for cuts The year against which countries measure their target decrease of emissions. The Kyoto Protocol uses a baseline year of 1990. Some countries prefer to use later baselines. Climate change legislation in the United States, for example, uses a 2005 baseline.

Biofuel A fuel derived from renewable, biological sources, including crops such as maize and sugar cane, and some forms of waste.

Black carbon The soot that results from the incomplete combustion of fossil fuels, biofuels, and biomass (wood, animal dung, etc.). It is the most potent climate-warming aerosol. Unlike greenhouse gases, which trap infrared radiation that is already in the Earth's atmosphere, these particles absorb all wavelengths of sunlight and then re-emit this energy as infrared radiation.

Business as usual A scenario used for projections of future emissions assuming no action, or no new action, is taken to mitigate the problem. Some countries are pledging not to reduce their emissions but to make reductions compared to a business as usual scenario. Their emissions, therefore, would increase but less than they would have done.

C

Cap and trade An emission trading scheme whereby businesses or countries can buy or sell allowances to emit greenhouse gases via an exchange. The volume of allowances issued adds up to the limit, or cap, imposed by the authorities.

Carbon capture and storage The collection and transport of concentrated carbon dioxide gas from large emission sources, such as power plants. The gases are then injected into deep underground reservoirs. Carbon capture is sometimes referred to as geological sequestration.

Carbon dioxide (CO2) Carbon dioxide is a gas in the Earth's atmosphere. It occurs naturally and is also a by-product of human activities such as burning fossil fuels. It is the principal greenhouse gas produced by human activity.

Carbon dioxide (CO2) equivalent Six greenhouse gases are limited by the Kyoto Protocol and each has a different global warming potential. The overall warming effect of this cocktail of gases is often expressed in terms of carbon dioxide equivalent - the amount of CO2 that would cause the same amount of warming.

Carbon footprint The amount of carbon emitted by an individual or organisation in a given period of time, or the amount of carbon emitted during the manufacture of a product.

Carbon intensity A unit of measure. The amount of carbon emitted by a country per unit of Gross Domestic Product.

Carbon leakage A term used to refer to the problem whereby industry relocates to countries where emission regimes are weaker, or non-existent.

Carbon neutral A process where there is no net release of CO2. For example, growing biomass takes CO2 out of the atmosphere, while burning it releases the gas again. The process would be carbon neutral if the amount taken out and the amount released were identical. A company or country can also achieve carbon neutrality by means of carbon offsetting.

Carbon offsetting A way of compensating for emissions of CO2 by participating in, or funding, efforts to take CO2 out of the atmosphere. Offsetting often involves paying another party, somewhere else, to save emissions equivalent to those produced by your activity.

Carbon sequestration The process of storing carbon dioxide. This can happen naturally, as growing trees and plants turn CO2 into biomass (wood, leaves, and so on). It can also refer to the capture and storage of CO2 produced by industry. See Carbon capture and storage.

Carbon sink Any process, activity or mechanism that removes carbon from the atmosphere. The biggest carbon sinks are the world's oceans and forests, which absorb large amounts of carbon dioxide from the Earth's atmosphere.

Certified Emission Reduction (CER) A greenhouse gas trading credit, under the UN Clean Development Mechanism programme. A CER may be earned by participating in emission reduction programmes - installing green technology, or planting forests - in developing countries. Each CER is equivalent to one tonne of carbon dioxide.

CFCs The short name for chlorofluorocarbons - a family of gases that have contributed to stratospheric ozone depletion, but which are also potent greenhouse gases. Emissions of CFCs around the developed world are being phased out due to an international control agreement, the 1989 Montreal Protocol.

Clean coal technology Technology that enables coal to be burned without emitting CO2. Some systems currently being developed remove the CO2 before combustion, others remove it afterwards. Clean coal technology is unlikely to be widely available for at least a decade.

Clean Development Mechanism (CDM) A programme that enables developed countries or companies to earn credits by investing in greenhouse gas emission reduction or removal projects in developing countries. These credits can be used to offset emissions and bring the country or company below its mandatory target.

Climate change A pattern of change affecting global or regional climate, as measured by yardsticks such as average temperature and rainfall, or an alteration in frequency of extreme weather conditions. This variation may be caused by both natural processes and human activity. Global warming is one aspect of climate change.

CO2 See carbon dioxide.

Country in transition Broadly speaking, any ex-Soviet bloc state. At the time the Kyoto Protocol was adopted in 1997, these countries were on the path from a Communist planned economy to a market economy. Many of them would now be categorised as market economies. Countries in transition to a market economy are grouped with industrialised countries in Annex I of the Kyoto Protocol, so they have emission reduction commitments to meet in the 2008-2012 period. In some cases their industrial base collapsed to such a degree in the early 1990s that they will have no difficulty meeting these commitments.

D

Dangerous climate change A term referring to severe climate change that will have a negative effect on societies, economies, and the environment as a whole. The phrase was introduced by the 1992 UN Framework Convention on Climate Change, which aims to prevent "dangerous" human interference with the climate system.

Deforestation The permanent removal of standing forests that can lead to significant levels of carbon dioxide emissions.

E

Emission Trading Scheme (ETS) A scheme set up to allow the trading of emissions permits between business and/or countries as part of a cap and trade approach to limiting greenhouse gas emissions. The best-developed example is the EU's trading scheme, launched in 2005. See Cap and trade.

EU Burden-sharing agreement A political agreement that was reached to help the EU reach its emission reduction targets under the Kyoto Protocol (a reduction of 8% during the period 2008-2012, on average, compared with 1990 levels). The 1998 agreement divided the burden unequally amongst member states, taking into account national conditions, including greenhouse gas emissions at the time, the opportunity for reducing them, and countries' levels of economic development.

F

Feedback loop In a feedback loop, rising temperatures on the Earth change the environment in ways that affect the rate of warming. Feedback loops can be positive (adding to the rate of warming), or negative (reducing it). The melting of Arctic ice provides an example of a positive feedback process. As the ice on the surface of the Arctic Ocean melts away, there is a smaller area of white ice to reflect the Sun's heat back into space and more open, dark water to absorb it. The less ice there is, the more the water heats up, and the faster the remaining ice melts.

Flexible mechanism Instruments that help countries and companies meet emission reduction targets by paying others to reduce emissions for them. The mechanism in widest use is emissions trading, where companies or countries buy and sell permits to pollute. The Kyoto Protocol establishes two flexible mechanisms enabling rich countries to fund emission reduction projects in developing countries - Joint Implementation (JI) and the Clean Development Mechanism (CDM).

Fossil fuels Natural resources, such as coal, oil and natural gas, containing hydrocarbons. These fuels are formed in the Earth over millions of years and produce carbon dioxide when burnt.

G

G77 The main negotiating bloc for developing countries, allied with China (G77+China). The G77 comprises 130 countries, including India and Brazil, most African countries, the grouping of small island states (Aosis), the Gulf states and many others, from Afghanistan to Zimbabwe.

Geological sequestration The injection of carbon dioxide into underground geological formations. When CO2 is injected into declining oil fields it can help to recover more of the oil.

Global average temperature The mean surface temperature of the Earth measured from three main sources: satellites, monthly readings from a network of over 3,000 surface temperature observation stations and sea surface temperature measurements taken mainly from the fleet of merchant ships, naval ships and data buoys.

Global energy budget The balance between the Earth's incoming and outgoing energy. The current global climate system must adjust to rising greenhouse gas levels and, in the very long term, the Earth must get rid of energy at the same rate at which it receives energy from the sun.

Global dimming An observed widespread reduction in sunlight at the surface of the Earth, which varies significantly between regions. The most likely cause of global dimming is an interaction between sunlight and microscopic aerosol particles from human activities. In some regions, such as Europe, global dimming no longer occurs, thanks to clean air regulations.

Global warming The steady rise in global average temperature in recent decades, which experts believe is largely caused by man-made greenhouse gas emissions. The long-term trend continues upwards, they suggest, even though the warmest year on record, according to the UK's Met Office, is 1998.

Global Warming Potential (GWP) A measure of a greenhouse gas's ability to absorb heat and warm the atmosphere over a given time period. It is measured relative to a similar mass of carbon dioxide, which has a GWP of 1.0. So, for example, methane has a GWP of 25 over 100 years, the metric used in the Kyoto Protocol. It is important to know the timescale, as gases are removed from the atmosphere at different rates.

Greenhouse gases (GHGs) Natural and industrial gases that trap heat from the Earth and warm the surface. The Kyoto Protocol restricts emissions of six greenhouse gases: natural (carbon dioxide, nitrous oxide, and methane) and industrial (perfluorocarbons, hydrofluorocarbons, and sulphur hexafluoride).

Greenhouse effect The insulating effect of certain gases in the atmosphere, which allow solar radiation to warm the earth and then prevent some of the heat from escaping. See also Natural greenhouse effect.

H

Hockey stick The name given to a graph published in 1998 plotting the average temperature in the Northern hemisphere over the last 1,000 years. The line remains roughly flat until the last 100 years, when it bends sharply upwards. The graph has been cited as evidence to support the idea that global warming is a man-made phenomenon, but some scientists have challenged the data and methodology used to estimate historical temperatures. (It is also known as MBH98 after its creators, Michael E. Mann, Raymond S. Bradley and Malcolm K. Hughes.)

I

IPCC The Intergovernmental Panel on Climate Change is a scientific body established by the United Nations Environment Programme and the World Meteorological Organization. It reviews and assesses the most recent scientific, technical, and socio-economic work relevant to climate change, but does not carry out its own research. The IPCC was honoured with the 2007 Nobel Peace Prize.

J

Joint implementation (JI) An agreement between two parties whereby one party struggling to meet its emission reductions under the Kyoto Protocol earns emission reduction units from another party's emission removal project. The JI is a flexible and cost-efficient way of fulfilling Kyoto agreements while also encouraging foreign investment and technology transfer.

K

Kyoto Protocol A protocol attached to the UN Framework Convention on Climate Change, which sets legally binding commitments on greenhouse gas emissions. Industrialised countries agreed to reduce their combined emissions to 5.2% below 1990 levels during the five-year period 2008-2012. It was agreed by governments at a 1997 UN conference in Kyoto, Japan, but did not legally come into force until 2005. A different set of countries agreed a second commitment period in 2013 that will run until 2020.

L

LDCs Least Developed Countries represent the poorest and weakest countries in the world. The current list of LDCs includes 49 countries - 33 in Africa, 15 in Asia and the Pacific, and one in Latin America.

LULUCF This refers to Land Use, Land-Use Change, and Forestry. Activities in LULUCF provide a method of offsetting emissions, either by increasing the removal of greenhouse gases from the atmosphere (i.e. by planting trees or managing forests), or by reducing emissions (i.e. by curbing deforestation and the associated burning of wood).

M

Major Economies Forum on Energy and Climate A forum established in 2009 by US President Barack Obama to discuss elements of the agreement that will be negotiated at Copenhagen. Its members - Australia, Brazil, Canada, China, the European Union, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, South Africa, South Korea, the UK and the US - account for 80% of greenhouse gas emissions. The forum is a modification of the Major Economies Meeting started by the former President George Bush, which was seen by some countries as an attempt to undermine UN negotiations.

Methane Methane is the second most important man-made greenhouse gas. Sources include both the natural world (wetlands, termites, wildfires) and human activity (agriculture, waste dumps, leaks from coal mining).

Mitigation Action that will reduce man-made climate change. This includes action to reduce greenhouse gas emissions or absorb greenhouse gases in the atmosphere.

N

Natural greenhouse effect The natural level of greenhouse gases in our atmosphere, which keeps the planet about 30C warmer than it would otherwise be - essential for life as we know it. Water vapour is the most important component of the natural greenhouse effect.

Non-annex I countries The group of developing countries that have signed and ratified the Kyoto Protocol. They do not have binding emission reduction targets.

O

Ocean acidification The ocean absorbs approximately one-fourth of man-made CO2 from the atmosphere, which helps to reduce adverse climate change effects. However, when the CO2 dissolves in seawater, carbonic acid is formed. Carbon emissions in the industrial era have already lowered the pH of seawater by 0.1. Ocean acidification can decrease the ability of marine organisms to build their shells and skeletal structures and kill off coral reefs, with serious effects for people who rely on them as fishing grounds.

P

Per-capita emissions The total amount of greenhouse gas emitted by a country per unit of population.

ppm (350/450) An abbreviation for parts per million, usually used as short for ppmv (parts per million by volume). The Intergovernmental Panel on Climate Change (IPCC) suggested in 2007 that the world should aim to stabilise greenhouse gas levels at 450 ppm CO2 equivalent in order to avert dangerous climate change. Some scientists, and many of the countries most vulnerable to climate change, argue that the safe upper limit is 350ppm. Current levels of CO2 only are about 380ppm.

Pre-industrial levels of carbon dioxide The levels of carbon dioxide in the atmosphere prior to the start of the Industrial Revolution. These levels are estimated to be about 280 parts per million (by volume). The current level is around 380ppm.

R

Renewable energy Renewable energy is energy created from sources that can be replenished in a short period of time. The five renewable sources used most often are: biomass (such as wood and biogas), the movement of water, geothermal (heat from within the earth), wind, and solar.

REDD Reducing Emissions from Deforestation and forest Degradation, a concept that would provide developing countries with a financial incentive to preserve forests.

S

Stern review A report on the economics of climate change led by Lord Nicholas Stern, a former World Bank economist. It was published on 30 October 2006 and argued that the cost of dealing with the consequences of climate change in the future would be higher than taking action to mitigate the problem now.

Tipping point A tipping point is a threshold for change, which, when reached, results in a process that is difficult to reverse. Scientists say it is urgent that policy makers halve global carbon dioxide emissions over the next 50 years or risk triggering changes that could be irreversible.

Twenty-twenty-twenty (20-20-20) This refers to a pledge by the European Union to reach three targets by 2020: (a) a 20% reduction in greenhouse gas emissions from 1990 levels; (b) an increase in the use of renewable energy to 20% of all energy consumed; and (c) a 20% increase in energy efficiency. The EU says it will reduce emissions by 30%, by 2020, if other developed countries also pledge tough action.

U

UNFCCC The United Nations Framework Convention on Climate Change is one of a series of international agreements on global environmental issues adopted at the 1992 Earth Summit in Rio de Janeiro. The UNFCCC aims to prevent "dangerous" human interference with the climate system. It entered into force on 21 March 1994 and has been ratified by 192 countries.

W

Weather The state of the atmosphere with regard to temperature, cloudiness, rainfall, wind and other meteorological conditions. It is not the same as climate which is the average weather over a much longer period.

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